Not long ago, Abdul Qadeer Khan used to walk into a wooded park across the street from his mansion in Pakistan's capital city and feed the monkeys who lived there. That was when he was a national hero and a multimillionaire, owner of a fleet of vintage cars and properties from Dubai to Timbuktu. But Khan, 68, no longer crosses the street to feed the monkeys. These days he is almost never seen outside. His house, which lies just over a grassy hillside from Islamabad's King Faisal Mosque, is modern, squat and dark, its façade concealed behind a vine-covered wall. To the casual observer, the house provides just one clue to its owner's sinister profession. At the end of his driveway sits a large jasmine bush, trimmed into an odd but unmistakable shape: that of a mushroom cloud.

When President George W. Bush identified the main threats to global security in his State of the Union address last week, the name A.Q. Khan was not on the list. In some respects, that's not surprising. Khan is under house arrest, his every move monitored by Pakistani government agents. He is said to be in failing health, and will probably live out his days a recluse. And yet one year after Khan appeared on Pakistani television and confessed to selling some of that country's most prized secrets, the world is only beginning to uncover the extent of his treachery--and comprehend how one man did more to destabilize the planet than did many of the world's worst regimes.

For more than a decade, Khan, the father of Pakistan's nuclear bomb, masterminded a vast, clandestine and hugely profitable enterprise whose mission boiled down to this: selling to a rogues' gallery of nations the technology and equipment to make nuclear weapons. Among Khan's customers were Iran and North Korea--two countries identified by Bush as members of the "axis of evil," whose nuclear ambitions present the U.S. with two of its biggest foreign policy quandaries. At a moment when the international community is focused on a potential showdown with Iran, a TIME investigation has revealed that Khan's network played a bigger role in helping Tehran and Pyongyang than had been previously disclosed. U.S. intelligence officials believe Khan sold North Korea much of the material needed to build a bomb, including high-speed centrifuges used to enrich uranium and the equipment required to manufacture more of them. Officials are worried--but have not yet seen proof--that Khan gave those countries rudimentary but effective designs for nuclear warheads. Officials in Washington and at the International Atomic Energy Agency (IAEA) in Vienna say they suspect that Iran may have bought the same set of goods--centrifuges and possibly weapons designs--from Khan in the mid-1990s. Although the IAEA says so far it has not found definitive proof that Iran has a weapons program, its investigators told TIME that Tehran has privately confirmed at least 13 meetings from 1994 to 1999 with representatives of Khan's network.